A Novel Les-Based Process for NOx Emission Assessment in a Premixed Swirl Stabilized Combustion System

2021 ◽  
Author(s):  
Roberto Meloni ◽  
Antonio Andreini ◽  
Pier Carlo Nassini
Keyword(s):  
Turbulent Flame ◽  
Nox Emission ◽  
Percentage Error ◽  
Nox Formation ◽  
Fuel Gas ◽  
Turbulent Flame Speed ◽  
Eddy Simulation ◽  
Annular Combustor ◽  
Swirl Stabilized Combustion ◽  
The Impact

Abstract This paper presents a new CFD approach for the assessment of the NOx emission. The methodology is validated against the experimental data of a heavy-duty gas turbine annular combustor. Since the NOx formation involves time scales that are different from the fuel oxidation time, the present work defines the transport equation source terms for NOx on the basis of a dedicate NOx-Damköhler number. The latter parameter allows to properly distinguish the "in-flame" contribution from the "post-flame" one. While the former is a mix of several mechanisms (prompt, N2O-pathway, thermal), the latter is dominated by the thermal contribution. The validation phase is developed in a Large-Eddy Simulation (LES) framework where the Extended Turbulent Flame Speed model is implemented to consider the influence of both heat loss and strain rate on the progress variable source term. The accuracy of the model against the most important operability parameters of the combustor is verified. A strong focus on the fuel composition effect onto NOx is presented as well. For any simulated operating condition, the present methodology is able to provide a limited percentage error if compared with the data, considering also different combustion regimes. Leveraging this alignment, the last portion of the paper is dedicated to a detailed post processing highlighting the role of some key factors on to NOx formation. In particular, the focus will be dedicated to the impact of the fuel gas composition and the pilot split.

A Novel LES-Based Process for NOx Emission Assessment in a Premixed Swirl Stabilized Combustion System

2021 ◽  
Author(s):  
R. Meloni ◽  
A. Andreini ◽  
P. C. Nassini
Keyword(s):  
Turbulent Flame ◽  
Nox Emission ◽  
Percentage Error ◽  
Nox Formation ◽  
Fuel Gas ◽  
Turbulent Flame Speed ◽  
Eddy Simulation ◽  
Annular Combustor ◽  
Swirl Stabilized Combustion ◽  
The Impact

Abstract This paper presents a new CFD approach for the assessment of the NOx emission. The methodology is validated against the experimental data of a heavy-duty gas turbine annular combustor. Since the NOx formation involves time scales that are different from the fuel oxidation time, the present work defines the transport equation source terms for NOx on the basis of a dedicate NOx-Damköhler number. The latter parameter allows to properly distinguish the “in-flame” contribution from the “post-flame” one. While the former is a mix of several mechanisms (prompt, N2O-pathway thermal), the latter is dominated by the thermal contribution. The validation phase is developed in a Large-Eddy Simulation (LES) framework where the Extended Turbulent Flame Speed model is implemented to consider the influence of both heat loss and strain rate on the progress variable source term. The accuracy of the model against the most important operability parameters of the combustor is verified. A strong focus on the fuel composition effect onto NOx is presented as well. For any simulated operating condition, the present methodology is able to provide a limited percentage error if compared with the data, considering also different combustion regimes. Leveraging this alignment, the last portion of the paper is dedicated to a detailed post processing highlighting the role of some key factors on to NOx formation. In particular, the focus will be dedicated to the impact of the fuel gas composition and the pilot split.

Co Emission Modeling in a Heavy Duty Annular Combustor Operating with Natural Gas

2021 ◽  
Author(s):  
Roberto Meloni ◽  
Stefano Gori ◽  
Antonio Andreini ◽  
Pier Carlo Nassini
Keyword(s):  
Turbulent Flame ◽  
Flame Temperature ◽  
Production Region ◽  
Turbulent Flame Speed ◽  
Eddy Simulation ◽  
Extinction Limit ◽  
Flamelet Generated Manifold ◽  
Annular Combustor ◽  
Definition Of ◽  
Co Emission

Abstract The present paper summarizes the development of a Large-Eddy Simulation (LES) based approach for the prediction of CO emission in an industrial gas turbine combustor. Since the operating point of the modern combustors is really close to the extinction limit, the availability of a tool able to detect the onset of high-CO production can be useful for the proper definition of the combustion chamber air split or to introduce design improvements for the premixer itself. The accurate prediction of CO cannot rely on the flamelet assumption, representing the fundament of the modern combustion models. Consequently, in this work, the Extended Turbulent Flame Speed Closure (ETFSC) of the standard Flamelet Generated Manifold (FGM) model is employed to consider the effect of the heat loss and the strain rate on the flame brush. Moreover, a customized CO-Damköhler number is introduced to de-couple the in-flame CO production region from the post-flame contribution where the oxidation takes place. A fully premixed burner working at representative values of pressure and flame temperature of an annular combustor is selected for the validation phase of the process. The comparison against the experimental data shows that the process is not only able to capture the trend but also to predict CO in a quantitative manner. In particular, the interaction between the flame and the air fluxes at some critical sections of the combustor, leading the CO emission from the equilibrium value to the super-equilibrium, has been correctly reproduced.

CO Emission Modeling in a Heavy Duty Annular Combustor Operating With Natural Gas

2021 ◽  
Author(s):  
R. Meloni ◽  
S. Gori ◽  
A. Andreini ◽  
P. C. Nassini
Keyword(s):  
Turbulent Flame ◽  
Flame Temperature ◽  
Production Region ◽  
Turbulent Flame Speed ◽  
Eddy Simulation ◽  
Extinction Limit ◽  
Flamelet Generated Manifold ◽  
Annular Combustor ◽  
Definition Of ◽  
Co Emission

Abstract The present paper summarizes the development of a Large-Eddy Simulation (LES) based approach for the prediction of CO emission in an industrial gas turbine combustor. Since the operating point of the modern combustors is really close to the extinction limit, the availability of a tool able to detect the onset of high-CO production can be useful for the proper definition of the combustion chamber air split or to introduce design improvements for the premixer itself. The accurate prediction of CO cannot rely on the flamelet assumption, representing the fundament of the modern combustion models. Consequently, in this work, the Extended Turbulent Flame Speed Closure (ETFSC) of the standard Flamelet Generated Manifold (FGM) model is employed to consider the effect of the heat loss and the strain rate on the flame brush. Moreover, a customized CO-Damköhler number is introduced to de-couple the in-flame CO production region from the post-flame contribution where the oxidation takes place. A fully premixed burner working at representative values of pressure and flame temperature of an annular combustor is selected for the validation phase of the process. The comparison against the experimental data shows that the process is not only able to capture the trend but also to predict CO in a quantitative manner. In particular, the interaction between the flame and the air fluxes at some critical sections of the combustor, leading the CO emission from the equilibrium value to the super-equilibrium, has been correctly reproduced.

Hybrid RANS/LES Simulation of a Lean Premixed Swirl Burner Based on a Turbulent Flame Speed Closure

2009 ◽  
Author(s):  
Guido Ku¨nne ◽  
Christian Klewer ◽  
Johannes Janicka
Keyword(s):  
Hybrid Methods ◽  
Turbulent Flame ◽  
Computational Cost ◽  
Flame Speed ◽  
Model Parameters ◽  
Detached Eddy Simulation ◽  
Combustion Modeling ◽  
Turbulent Flame Speed ◽  
Eddy Simulation ◽  
The Impact

In this work, simulations of a strongly swirled premixed flame at atmospheric pressure were carried out using classical RANS-methods as well as different hybrid RANS/LES approaches. In the context of RANS, a large number of simulations using the k-ε-model were performed to study the impact of sensitivities related to boundary conditions and model parameters. For the transient simulations, the hybrid methods, DES (Detached Eddy Simulation) and SAS (Scale Adaptive Simulation) as implemented in ANSYS-CFX, were employed. These methods were used to avoid the prohibitive computational cost of LES in boundary layers but to resolve the detached eddies to capture the flame turbulence interaction. Combustion modeling in CFX is based on a transport equation for the progress variable combined with a turbulent flame speed closure to treat the chemical source term. In addition, isothermal LES was performed in advance to identify the coherent structures, such as precessing vortex cores, which were observed experimentally.

Combustion Characteristics and NOX Emission of Hydrogen-Rich Fuel Gases at Gas Turbine Relevant Conditions

2012 ◽  
Author(s):  
Y.-C. Lin ◽  
S. Daniele ◽  
P. Jansohn ◽  
K. Boulouchos
Keyword(s):  
Gas Turbine ◽  
Turbulent Combustion ◽  
Turbulent Flame ◽  
Elevated Pressure ◽  
Chemical Kinetic ◽  
Nox Emission ◽  
Operating Pressure ◽  
High Hydrogen ◽  
Turbulent Flame Speed ◽  
Fuel Mixtures

In this paper, characteristics of turbulent combustion and NOx emission for high hydrogen-content fuel gases (H2 > 70 vol. %; “hydrogen-rich”) are addressed. An experimental investigation is performed in a perfectly-premixed axial-dump combustor under gas turbine relevant conditions. Fundamental features of turbulent combustion for these mixtures are evaluated based on OH-PLIF diagnostics. On the other hand, NOx emissions are measured with an exhaust gas sampling probe positioned downstream the combustor outlet. Compared to syngas mixtures (H2 + CO), the operational limits for hydrogen-rich fuel gases are found to occur at even leaner conditions concerning flashback phenomena. With respect to effects of operating pressure, a strongly reduced operational envelope is observed at elevated pressure. Only with decreasing the preheat temperature a viable approach to further extend the operational range is seen. Evaluation of the averaged turbulent flame shape shows that the profile of the flame front is generally approaching that of an ideal cone. Thus a simplified approach for estimating the turbulent flame speed via the location of the flame tip alone can be applied. The level of NOx emission for the hydrogen-rich fuel mixtures is generally above that of syngas mixtures, which exhibit already higher NOx emission values than natural gas. Distinct chemical kinetic features are found specifically at elevated pressure. While the pressure effects are weak for syngas, a non-monotonic behavior is observed for the hydrogen-rich fuels. Reaction path analysis is performed to complement and provide more insight to the findings from the measurements. From chemical kinetic calculations a distinct shift in NOx formation pathways (thermal NOx vs. NOx through N2O/NNH reaction channels) can be observed for the different fuel mixtures at different pressure levels.

An Optimized Correlation for Turbulent Flame Speed for C1-C3 Fuels at Engines-Relevant Conditions

2020 ◽  
Author(s):  
Eoin M. Burke ◽  
Sajjad Yousefian ◽  
Felix Güthe ◽  
Rory F. D. Monaghan
Keyword(s):  
Entire Range ◽  
State Of The Art ◽  
Velocity Ratio ◽  
Turbulent Flame ◽  
Search Method ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Percentage Error ◽  
Turbulent Flame Speed ◽  
Wide Range

Abstract The aim of this work is to examine the state-of-the-art turbulent flame speed (ST) correlations and optimize their adjustable parameters to best match a wide range experimental turbulent premixed combustion results. Four correlations based on previous works by Zimont, Kobayashi, Ronney and Muppala have been selected for the present study. Using a Matlab-based Nelder-Mead simplex direct search method, each correlation’s adjustable parameters are optimized such that their mean absolute percentage error (MAPE) is minimized. In addition to the literature correlations, a new empirical correlation is developed using the same search method to define constants and powers in the expression. Two sets of optimized parameters are proposed to account for atmospheric and elevated (0.2–3.0 MPa) pressure flames. Each correlation is tested further, examining their ability to match ST trends for varying equivalence ratio (φ) and turbulent velocity ratio (u′/SL). It was found that a minimum of two correlations and two sets of adjustable parameters are required to accurately account for the entire range of data, thus showing that there is currently no turbulent flame speed correlation that is applicable across all engine-relevant conditions.

An Optimized Correlation for Turbulent Flame Speed for C1–C3 Fuels at Engine-Relevant Conditions

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Sajjad Yousefian ◽  
Eoin M. Burke ◽  
Felix Güthe ◽  
Rory F. D. Monaghan
Keyword(s):  
Entire Range ◽  
State Of The Art ◽  
Velocity Ratio ◽  
Turbulent Flame ◽  
Search Method ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Percentage Error ◽  
Turbulent Flame Speed ◽  
Wide Range

Abstract The aim of this work is to examine the state-of-the-art turbulent flame speed (ST) correlations and optimize their adjustable parameters to best match a wide range experimental turbulent premixed combustion results. Based on previous work, four correlations have been selected for this study. Using a matlab-based Nelder–Mead simplex direct search method, each correlation's adjustable parameters are optimized such that their mean absolute percentage error (MAPE) is minimized. In addition to the literature correlations, a new empirical correlation is developed using the same search method to define constants and powers in the expression. Two sets of optimized parameters are proposed to account for atmospheric and elevated (0.2–3.0 MPa) pressure flames. Each correlation is tested further, examining their ability to match ST trends for varying equivalence ratio (φ) and turbulent velocity ratio (u′/SL). It was found that a minimum of two correlations and two sets of adjustable parameters are required to accurately account for the entire range of data, thus showing that there is currently no turbulent flame speed correlation that is applicable across all engine-relevant conditions.

Investigation of H2/CH4-Air Flame Characteristics of a Micromix Model Burner at Atmosphere Pressure Condition

2018 ◽  
Author(s):  
Xunwei Liu ◽  
Weiwei Shao ◽  
Yong Tian ◽  
Yan Liu ◽  
Bin Yu ◽  
...  
Keyword(s):  
Hydrogen Content ◽  
Gas Turbines ◽  
Turbulent Flame ◽  
Experimental Studies ◽  
Nox Emission ◽  
Inlet Temperature ◽  
Nox Emissions ◽  
High Hydrogen ◽  
Atmosphere Pressure ◽  
Turbulent Flame Speed

For high-hydrogen-content fuel, the Micromix Combustion Technology has been developed as a potential low NOx emission solution for gas turbine combustors, especially for advanced gas turbines with high turbine inlet temperature. Compared with conventional lean premixed flames, multiple distributed slim and micro flames could lead to a lower NOx emission performance for shortening residence time of high temperature flue gas and generally a more uniform temperature distribution. This work aims at micromix flame characteristics of a model burner fueled with hydrogen blending with methane under atmosphere pressure conditions. The model burner assembly was designed to have six concentrically millimeter-sized premixed units around a same unit centrally. Numerical and experimental studies were conducted on mixing performance, flame stability, flame structure and CO/NOx emissions of the model burner. OH radical distribution by OH-PLIF and OH chemiluminescence (OH*) imaging were employed to analyze the turbulence-reaction interactions and characters of the reaction zone at the burner exit. Micromix flames fueled with five different hydrogen content H2-CH4 (60/40, 50/50, 40/60, 30/70, 0/100 Vol.%) were investigated, along with the effects of equivalence ratio and heat load. Results indicated that low NOx emissions of less than 10 ppm (@15% O2) below the exhaust temperature of 1920 K were obtained for all the different fuels. Combustion oscillation didn’t occur for all the conditions. It was found that at a constant flame temperature, the higher the hydrogen content of the fuel, the higher the turbulent flame speed and the weaker the flame lift effect. Combustion noise and NOx emissions also increase with increasing hydrogen content. The OH/OH* signal distribution indicated that a pure methane micromix flame showed a lifted and weaken distributed feature.

Investigation of the Turbulent Flame Speed for Natural Gas and Natural Gas/Hydrogen Mixtures at High Turbulence Levels and Volumetric Heat Release Rates

2013 ◽  
Author(s):  
Martin Zajadatz ◽  
Nikolaos Zarzalis ◽  
Wolfgang Leuckel
Keyword(s):  
Natural Gas ◽  
Heat Release ◽  
Gas Turbines ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Release Rates ◽  
Fuel Gas ◽  
Lean Premixed Combustion ◽  
Number Range ◽  
Turbulent Flame Speed

In gas turbine combustion application, there is a strong tendency towards high volumetric heat release rates without compromising ignition stability and the requirement of low emission concentrations of NOx, CO and unburned hydrocarbons. In order to meet these demands for industrial gas turbines the lean premixed combustion concept has been developed. In the scope of this paper fundamental experimental work, which has been carried out in order to analyze the important topic of turbulence/chemistry interaction on a semi-technical scale, will be reported. The turbulent intensity and length scales have been varied by a generic burner system, which consists of four geometrically scaled burners. At atmospheric pressure conditions more than 700 Bunsen type flames in a Reynolds number range from 21000 to 128000 have been investigated. Gas/air mixture preheating has been included in the tests as a typical boundary condition for combustion in gas turbines. The natural gas was blended with 25 vol. % and 50 vol. % hydrogen in order to alter the kinetics of the fuel gas. The influence of the aforementioned parameters on the turbulent flame speed were assessed and compared with existing correlations for the turbulent flame speed. Special emphasis has been taken on the influence of gas/air mixture preheating and kinetics.

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